98 THE NAUTILUS. 



peninsula from Saginaw Bay on the Lake Huron shore to nearly as 

 far south on the Lake Michigan coast. This form is the character- 

 istic Pliysa of the lake shore, and is commonly found clinging to the 

 large stones along the rocky or stony beaches. Its thick wine-col- 

 ored or purplish shell with prominent white varicose bands, basally 

 expanded aperture, and the regularly curved outline from the apex 

 to the columella, give it an aspect peculiarly its own, and render it 

 easily distinguishable from the typical form or any of the allied 

 species. Specimens from the Beaver Islands, Lake Michigan and 

 Mackinaw City on the mainland, while retaining the peculiar form, 

 are thinner, more inclined to be horn-colored and have a narrower 

 marginal band, which internally is red rather than brown, and in 

 these respects seem to connect the variety with the typical form. 

 Were it not for these intermediate examples, there would be good 

 ground for considering the form worthy of specific rank. 

 Pliysa ancillaria var. crassa. 



Shell oval or obovate, thick, solid, opaque, smooth, shining, longi- 

 tudinal stria? very fine, transverse stria? minute or subobsolete ; white, 

 more or less tinged with vinous or pale purple ; darker toward the 

 apex, which is dark brown ; whorls 4-5 ; regularly and rapidly in- 

 creasing, the first minute, the last very large, roundly shouldered and 

 frequently flattened laterally ; spire short, scarcely elevated above 

 the general contour of the shell ; suture but slightly impressed, bor- 

 dered below with white ; aperture large, but slightly shorter than 

 the shell ; widest in the centre, somewhat narrowed below and 

 slightly effuse at the junction of the basal lip with the columella ; 

 outer lip broadly rounded, thin, acute, thickened within by a strong 

 callus which is yellowish-brown within and white externally ; inter- 

 ior of body whorl light yellowish-brown or liver color; extremities 

 of lip connected by a thin callus which is broadly reflected over the 

 body whorl ; columella strong, white, nearly straight, but slightly 

 twisted. 



Alt. 17^, diam. 12^, length of aperture 14 mm. 



Alt. 16, diam. 12^, length of aperture 13-| mm. 



Alt. 15, diam. 11, length of aperture 13^ mm. 



Higgins Lake, Roscommon County, Michigan. 



This form, while related to the variety magnalacustris in its tex- 

 ture, differs entirely in its shape, which is quite similar to the typical 

 form in the roundly-shouldered body whorl, and more elongated and 



